A sample is irradiated while being scanned with electrons, and secondary charged particles emitted from the sample are detected, thereby observing a structure on a surface of the sample. This is called a scanning electron microscope (hereinafter abbreviated as SEM). Moreover, a sample is irradiated with an electron beam after a negative potential as compared with an accelerating voltage of electrons is given to the sample, thereby imaging mirror electrons trajectories of which are reversed before colliding with the sample. This is called a mirror electron microscope (MEM). Furthermore, for example, a potential of approximately 20 V positive as compared with the accelerating voltage of electrons is given to the sample, and an irradiation electron beam collides with a sample surface with low energy and reflected electrons are imaged after the collision with the sample surface. This is called a low-energy emission electron microscope (LEEM). According to the above microscopes, ultrafine foreign matters or defects on the sample can be found. A mirror electron microscope is disclosed in Patent Document 1 and a low-energy emission electron microscope is disclosed in Patent Document 2.
As an imaging-type optical system is used particularly in MEM and LEEM, they are expected as high-speed inspection devices in manufacturing of electron devices as observation can be performed at higher speed as compared with SEM.
On the other hand, it is also possible to observe a structure on the sample surface by focusing an ion beam and irradiating the sample while being scanned with the ion beam to thereby detect secondary electrons, secondary ions, reflected ions and so on emitted from the sample. This is called a scanning ion microscope (hereinafter abbreviated as SIM). In Patent Literature 3, a scanning ion microscope using a liquid metal ion source is disclosed. In Patent Literature 4, a scanning ion microscope using a gas field ion source is disclosed.